1. Field of Invention
The present invention generally relates to respiratory sensor and alarm technology, and more particularly, relates to a dual mode respiratory airflow sensor and monitoring technology for the detection of any and all potentially life threatening respiratory events.
2. Description of Related Art
It is known in the art to monitor patients susceptible to disorders of the respiratory system, or in critical care settings, to employ respiration sensors and alarm systems. U.S. Pat. No. 4,878,502 issued to Dietz discusses a respiration airflow sensor employing a tube in which a ball is free to move, thereby breaking a beam of light. The ball is forced to move by the flow of air associated with the breathing of the patient. In U.S. Pat. No. 4,745,925 also issued to Dietz, another variation of an opthoelectric inhalation sensor using thin film deposition is discussed. Monitoring of respiration disorders by acoustic sensors is mentioned in U.S. Pat. No. 4,602,644 issued to DeBenedetto et al., and in U.S. Pat. No. 4,595,016 issued to Fertig et al. U.S. Pat. No. 4,366,821 issued to Wittmaier et al. shows a respiration monitoring system, which preferably uses a gas sensor. U.S. Pat. No. 4,350,166 issued to Mobarry shows an infant respiration detector of long wave infrared light which is absorbed by carbon dioxide. When an infant's exhalation (and thus its production of carbon dioxide) is interrupted, an alarm is activated. In U.S. Pat. No. 4,326,404 issued to Mehta, moisture is sensed using a sodium chloride crystal.
U.S. Pat. No. 4,306,867 issued to Krasner shows the use of a pressure sensor. An impedance plethysmograph is employed in U.S. Pat. No. 4,289,142 issued to Kearns. The use of thermoresistive sensors is suggested in U.S. Pat. No. 3,903,876 issued to Harris, U.S. Pat. No. 3,884,219 issued to Richardson et al., and U.S. Pat. No. 3,999,537 issued to Noiles. All of the above methods are complicated and expensive, or else unworkable in a real hospital setting for perioperative patients.
Pulse oximeters are also used on a patient's extremity, typically a finger, which monitor the oxygen content of a patient's blood through non-invasive means. However, a pulse oximeter can only detect hypoxia after the condition has arisen, i.e., after respiratory depression has occurred for a significant period of time.
Other possible solutions (and their associated problems) include capnographic end tidal CO2 monitors (highly accurate but prohibitively expensive), hemodynamic monitors which use Swan Ganz pulmonary artery catheters (expensive and have a high morbidity), and increased physician- or nurse-to-patient ratios (prohibitively expensive and inefficient).
There is thus a need in the field of perioperative healthcare for an inexpensive system and method of monitoring a patient's respiration that are reliable, workable, and practical in the typical perioperative environment.